The present invention relates to derivatives of [2-(8,9-dioxo-2,6-diazabicyclo[5.2.0]non-1(7)-en-2-yl)alkyl]phosphonic acid and methods of making them. The compounds of the present invention are particularly useful as N-methyl-D-aspartate (NMDA) receptor antagonists.
Glutamate and aspartate play dual roles in the central nervous system as essential amino acids and as the principal excitatory neurotransmitters. There are at least four classes of excitatory amino acid receptors: NMDA, AMPA (2-amino-3-(methyl-3-hydroxyisoxazol-4-yl)propanoic acid), kainate, and metabotropic receptors. These excitatory amino acid receptors regulate a wide range of signaling events that impact physiological brain functions. For example, activation of the NMDA receptor has been shown to be the central event that leads to excitotoxicity and neuronal death in many disease states, as well as a result of hypoxia and ischaemia following head trauma, stroke, and following cardiac arrest. It is also known that the NMDA receptor plays a major role in the synaptic plasticity that underlies many higher cognitive functions, such as memory and learning, certain nociceptive pathways, and in the perception of pain. In addition, certain properties of NMDA receptors suggest that they may be involved in the information-processing in the brain that underlies consciousness itself.
NMDA receptors are localized throughout the central nervous system. NMDA receptors are ligand-gated cation channels that modulate sodium, potassium, and calcium ions flux when they are activated by glutamate in combination with glycine. Structurally, the NMDA receptor is thought to be comprised of heteromultimeric channels containing two major subunits designated as NR1 and NR2. These subunits contain a glycine binding site, a glutamate binding site, and a polyamine binding site. For the NR1 subunit, multiple splice variants have been identified, whereas for the NR2 subunit, four individual subunit types (NR2A, NR2B, NR2C, and NR2D) have been identified. The NMDA receptor also contains an Mg++ binding site located inside the pore of the ionophore of the NMDA receptor/channel complex, which blocks the flow of ions.
Substantial preclinical and clinical evidence indicates that inhibitors of the NMDA receptor have therapeutic potential for treating numerous disorders. Disorders believed to be responsive to inhibition of NMDA receptors include cerebral vascular disorders, such as cerebral ischemia (e.g., stroke) or cerebral infarction resulting in a range of conditions, such as thromboembolic or hemorrhagic stroke, or cerebral vasospasm; cerebral trauma; muscular spasm; and convulsive disorders, such as epilepsy or status epilepticus. NMDA receptor antagonists may also be used to prevent tolerance to opiate analgesia or to help control symptoms of withdrawal from addictive drugs.
Screening of compounds in recent years have identified a number of NMDA receptor antagonists that have been used in animal and clinical human studies to demonstrate proof of concept for the treatment of a variety of disorders. The difficulty with demonstrating clinical utility of NMDA receptor antagonists has generally been the antagonists' lack of NMDA receptor subtype selectivity and/or biological activity, when dosed orally. Thus, the search for NMDA receptor antagonists that are subtype-selective and/or orally efficacious continues.